1. Field
Exemplary embodiments relate to a tungsten plug, a method of forming a tungsten plug and a semiconductor device having a tungsten plug. More particularly, exemplary embodiments relate to a seam-free tungsten plug, a method of forming a seam-free tungsten plug and a semiconductor device having a seam-free tungsten plug.
2. Description of the Related Art
A semiconductor memory device may be classified as either a volatile memory device or a non-volatile memory device. The volatile memory device requires power in order to maintain its stored information, unlike the non-volatile memory device which does not require that power be maintained in order to retain its data. Types or volatile memory devices include a DRAM (dynamic random access memory), a SRAM (static random access memory), etc. Types of non-volatile memory devices include a flash memory device, an EEPROM (electrically erasable programmable read only memory), etc.
Recently, a PRAM (phase-changeable random access memory), one type of non-volatile memory device, has been developed. The PRAM stores or erases data using a resistance between two states, a crystalline state and an amorphous state, by a phase transition. That is, the PRAM stores or erases data “1” and “0” using a reversible phase transition of a phase-changeable material layer, which typically includes germanium (Ge)-antimony (Sb)-tellurium (Te), and which is a chalcogenide material. For example, a reset current for converting a crystalline state into an amorphous state having a resistance larger than that of the crystalline state and a set current for converting an amorphous state into a crystalline state having a resistance smaller than that of the amorphous state may be transmitted from a diode to the phase-changeable material layer through a lower electrode. The lower electrode may be formed between the phase-changeable material layer and the diode. A metal silicide layer or a metal layer may be further formed between the diode and the lower electrode to reduce resistance of an interface therebetween.
As the size of a semiconductor memory device is decreased, the size of a region at which the diode and the lower electrode make contact with each other is also reduced. Because the region where the diode and the lower electrode make contact with each other is reduced, when a plug is formed in the region, a seam or a void may be generated in the region. When the seam or the void is exposed, it may be difficult to control a resistance of the plug.